1. Field of the Invention
The present invention relates to a surface light source device for use with a back-light or the like for back-lighting a transmissive display panel, and more particularly to an air-cooled structure for a surface light source device containing lamps for allowing for heat conduction.
2. Description of Related Art
A display panel, using liquid crystal or the like as an electro-optical substance in a large-sized flat display to replace CRT's, has been under development in recent years.
The display panel is not a spontaneous light emission type, but modulates external light to display a screen. The display panel can be roughly divided into transmission types and reflection types. In the case of the transmission type, a surface light source device is arranged on the back of the display panel for back-lighting.
A surface light source device used as a back-light for A large-sized display panel contains lamps consisting of a large number of fluorescent tubes or the like to generate a large amount of heat. This heat raises the temperature of the display panel to change the electro-optical characteristics of the liquid crystal used as electro-optical substance, thus deteriorating the image quality. Also, the atmospheric temperature within the back-light rises to decrease the luminous efficiency of the fluorescent tubes, causing deteriorated brightness. For this reason, forced cooling using air-cooling fans or like becomes indispensable in a large-sized back-light. If, however, an air-cooling fan is used, dust is whirled up to adhere to the surface of lamps or to a diffuser panel disposed thereon, thus deteriorating the uniformity of brightness of the surface light source device.
If dust stuck on the lamps and the diffuser panel is visually recognized by an observer through a transmissive display panel, the image quality will be noticeably deteriorated.